WM9090ECS/R Wolfson Microelectronics, WM9090ECS/R Datasheet - Page 73

• Manufacturer Part Number: WM9090ECS/R
• Description: Audio CODECs Audio Subsystem w/ capless headphones
• Manufacturer: Wolfson Microelectronics

Specifications of WM9090ECS/R

• Interface Type: 2-Wire, l2C
• Thd Plus Noise: 80 dB
• Ic Function: Ultra Low Power Audio Subsystem
• Brief Features: Mono Class D Speaker Driver, Automatic Gain Control (AGC)
• Supply Voltage Range: 2.7V To 5.5V
• Operating Temperature Range: -40°C To +85°C
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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Pre-Production
POWER SUPPLY DECOUPLING
Electrical coupling exists particularly in digital logic systems where switching in one sub-system
causes fluctuations on the power supply. This effect occurs because the inductance of the power
supply acts in opposition to the changes in current flow that are caused by the logic switching. The
resultant variations (or ‘spikes’) in the power supply voltage can cause malfunctions and
unintentional behavior in other components. A decoupling (or ‘bypass’) capacitor can be used as an
energy storage component which will provide power to the decoupled circuit for the duration of these
power supply variations, protecting it from malfunctions that could otherwise arise.
Coupling also occurs in a lower frequency form when ripple is present on the power supply rail
caused by changes in the load current or by limitations of the power supply regulation method. In
audio components such as the WM9090, these variations can alter the performance of the signal
path, leading to degradation in signal quality. A decoupling (or ‘bypass’) capacitor can be used to
filter these effects, by presenting the ripple voltage with a low impedance path that does not affect
the circuit to be decoupled.
These coupling effects are addressed by placing a capacitor between the supply rail and the
corresponding ground reference. In the case of systems comprising multiple power supply rails,
decoupling should be provided on each rail.
The recommended power supply decoupling capacitors for WM9090 are listed below in Table 36.
Table 36 Power Supply Decoupling Capacitors
Note: 0.1μF is required with 2.2μF a guide to the total required power rail capacitance.
All decoupling capacitors should be placed as close as possible to the WM9090 device. The
connection between GND, the AVDD decoupling capacitor and the main system ground should be
made at a single point as close as possible to the GND ball of the WM9090.
The VMID capacitor is not, technically, a decoupling capacitor. However, it does serve a similar
purpose in filtering noise on the VMID reference. The connection between GND, the VMID
decoupling capacitor and the main system ground should be made at a single point as close as
possible to the GND ball of the WM9090.
Due to the wide tolerance of many types of ceramic capacitors, care must be taken to ensure that the
selected components provide the required capacitance across the required temperature and voltage
ranges in the intended application. For most application the use of ceramic capacitors with capacitor
dielectric X5R is recommended.
HEADPHONE OUTPUT PATH
The headphone output on WM9090 is ground referenced and therefore does not require the large,
expensive capacitors necessary for VMID-referenced solutions. For best audio performance, it is
recommended to connect a zobel network to the audio output pins. This network should comprise of
a 100nF capacitor and 20ohm resistor in series with each other (see “Analogue Outputs” section).
These components have the effect of dampening high frequency oscillations or instabilities that can
arise outside the audio band under certain conditions. Possible sources of these instabilities include
the inductive load of a headphone coil or an active load in the form of an external line amplifier.
AVDD
SPKVDD
VMIDC
POWER SUPPLY
2.2μF ceramic
0.1μF ceramic (see note)
2.2μF ceramic (see text below)
DECOUPLING CAPACITOR
PP, January 2010, Rev 3.0
WM9090
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